Topaz at Stone Age Jewels

Topaz is a silicate mineral of aluminium and fluorine with the chemical formula Al2SiO4(F,OH)2. It crystallizes in the orthorhombic system and its crystals are mostly prismatic terminated by pyramidal and other faces, the basal pinacoid often being present. It has an easy and perfect basal cleavage, meaning that gemstones or other fine specimens have to be handled with care to avoid developing cleavage flaws. The fracture is conchoidal to uneven. Topaz has a hardness of 8, a specific gravity of 3.4–3.6, and a vitreous luster. Pure topaz is transparent but is usually tinted by impurities; typical topaz is wine or straw-yellow. They may also be white, gray, green, blue, pink or reddish-yellow and transparent or translucent. When heated, yellow topaz often becomes reddish-pink. Imperial Topaz

Topaz can also be irradiated, turning the stone blue, ranging from a light pure color to very dark almost electric blue. A recent trend in jewelry is the manufacture of topaz specimens that display iridescent colors, by applying a thin layer of titanium oxide via physical vapor deposition, this stone is then sold as 'mystic fire topaz'.

Topaz is commonly associated with silicic igneous rocks of the granite and rhyolite type. It typically crystallizes in granitic pegmatites or in vapor cavities in rhyolite lava flows like those at Topaz Mountain in western Utah. It may be found with fluorite and cassiterite. It can be found in the Ural and Ilmen mountains, Afghanistan, Czech Republic, Germany, Norway, Sherry-colored Topaz Pakistan, Italy, Sweden, Japan, Brazil, Mexico, and the United States.

Topaz crystals from Brazilian pegmatites are up to 80cm x 60cm x 60cm in size. The biggest topaz crystal ever found, named "El Dorado", was found in Brazil in 1984. It weighs 6.2 kg and belongs to the British Royal Collection.

The name "topaz" is derived from the Greek tòpazi[òs], which was the name of an island in the Red Sea that was difficult to find and from which a yellow stone (now believed to be chrysolite: yellowish olivine) was mined in ancient times; topaz itself (rather than topazios) wasn't really known before the classical era. In the Middle Ages the name topaz was used to refer to any yellow gemstone, but now the name is only properly applied to the silicate described above.

Many modern English translations of the Bible, including the King James Version mention topaz in Exodus 28:17 in reference to a stone in the Hoshen: "And thou shalt set in it settings of stones, even four rows of stones: the first row shall be a sardius, a topaz, and a carbuncle: this shall be the first row." However, since these translations as topaz all derive from the Septuagint translation tòpazi[òs], which as mentioned above referred to a yellow stone that wasn't topaz, probably chrysolite, it should be borne in mind that topaz is not meant here. The masoretic text (the Hebrew on which most modern bible translations of the Old Testament are based) has pitdah as the gem the stone is made from; pitdah is of unknown meaning, though scholars think it is related to an Assyrian word meaning flashed. There is a wide range of views among traditional sources regarding the Israelites tribal relativity thereto.

References: Hurlbut, Cornelius S.; Klein, Cornelis, 1985, Manual of Mineralogy, 20th ed., ISBN 0-471-80580-7
The Complete Encyclopedia of Minerals by P. Korbel and M. Novak

This extraordinary topaz gem is labeled 22,892.5 carats. It is displayed in the Smithsonian Museum of Natural History and it's origin is Minas Gerais, Brazil. It is cut with 172 facets and has a mass of 4.6 kg and measures about 15 cm across. It is classified as American golden topaz, and the composition is Al2SiO4 (F,OH)2, a silicate of aluminum.

Topaz has a hardness of 8 on the Moh's Scale.